Method of coating electrical contact pins



Patented July 10, 1951 METHOD OF COATING ELECTRICAL CONTACT PINS Anna Margareta Bergii-Heineman, Stockholm,

Sweden, assignor to Aktiebolaget Svenska Elektronror, Stockholm, Sweden, a corporation of Sweden No Drawing. Application February 14, 1947, Se-

rial No. 728,732. 1944 In Sweden December 23,

Section 1, Public Law 690, August 8, 1946 Patent expires December 23, 1964 2 Claims.

The present invention relates to a method for obtaining electrically well-conducting surfaces on contacting members and has been developed to improve the electrical conductivity of contact pins and the like of chrome-iron alloys for electrical discharge tubes, said contacting members becoming deteriorated by oxidation, for example, during some process in the manufacture of the tube so that undesirable changes and irregularities appear in the conductivity of the contact surface.

In the manufacture of radio tubes of the socalled press-moulded glass type, the contact pins usually consistof chrome-iron wires which during the compression of the base plate or the tube are sealed into the glass mass of the plate. In connection with the press moulding of the base plate the contact pins are subjected to a certain oxidation resulting in a considerable fluctuation of the contacting properties between pins of different tubes. Normally the oxide contaminants are eliminated by reduction by means of the flames sweeping the tube during its manufacture, but chrome oxide is not removed so easily. According to the invention, this inconvenience is overcome in such a manner that when the electrode system of the tube has been mounted on the base plate with its contact pins, the contact pins are covered, prior to the sealing of the tubular envelope, with zapon lacquer in which silver oxide has been suspended. In connection with the sealing of the envelope with the base plate the lacquer is burnt away and the silver oxide is reduced to metal. Probably the conversion of the silver oxide is a repeated process, the reduced silver reacting with the oxygen in the chrome oxide on the contact pins into silver oxide which again is dissociated into metallic silver etc. This effect of the silver oxide which in this connection may be considered essentially active as an autocatalyzer for the disintegration of the chrome oxide coating of the contact pins, results in the production of smooth bright contact pins of good contacting properties.

In some cases, however, certain difficulties may appear in getting the metal obtained by the heating of the compound to sinter sufficiently firmly together with the base especially if the thermal dissociation of the compound is eifected at too low a temperature respectively if the base is covered with a relatively strong oxide coating. It is proved, however, that a very good adhesion may be obtained by providing the compound dissociable into metal with an addition of lead borate. Bright contact surfaces can be produced by using a suspension of 3-25, preferably 8-15, parts by weight of silver oxide to one part by weight of lead borate (lead metaborate) in a suspender such as ethylene glycol or some other suitable medium, giving the whole a greasy condition for coating the contact surfaces. In the treatment of contact pins for discharge tubes very satisfactor results have been obtained with a coating mixture with the composition 20 parts by weight of silver oxide 2.5 parts by weight of lead metaborate 21 parts by weight of ethylene glycol.

For the preparation of the mixture the silver oxide was first ground in a ball mill for 24 hours, the silver oxide so treated then being ground in a mortar together with the lead borate until they were well mixed, whereupon ethylene glycol is added and a further grinding during a short time is performed. The contact pins are coated with the paste before the sealing of the stem with the tubular envelope.

The lead borate insures that the covering paste firmly sinters together with the base and that the well adhering layer shows a very good electrical conductivity on account of its great content of silver.

What I claim is:

1. The method of producing a surface having good electrical conducting characteristics on contact pins of a chrome-iron alloy sealed in electrical lamp bases by dissociating the chrome oxide layer formed on said pins when said bases are sealed which includes the steps of applying a silver oxide coating to the surfaces of said pins having said chromium oxide layer thereon and applying heat to said coating suflicient to dissociate said silver oxide to silver, to cause said silver to react with the chromium oxide to dissociate same, and to sinter the residual silver onto the surfaces of said contact pins.

2. The method as set forth in claim 1 which includes the additional step of mixing said silver oxide with a lead borate flux prior to application to said contact pins.

ANNA MARGARETA BERG -HEINEMAN.

(References on following page) REFERENCES CITED The following references are of record in the file of this patent:

"UNITED STATES PATENTS l Number Number 4 Name Date Smith Apr. 30, 1935 Box Oct. 14, 1947 FOREIGN PATENTS Country Date Great Britain Mar. 22, 1934 Sweden Oct. 12, 1948 

